Method of manufacturing pole piece assembly for electromagnetic type pickup

ABSTRACT

A method of manufacturing a pole piece assembly for an electromagnetic-type pickup is disclosed. In the method a pole piece unit including a set of pole pieces integrally interconnected with each other is first punched from a sheet of magnetic material and then the punched pole pieces are bent into a predetermined shape. The pole piece unit having the predetermined shape is next fixed to a fixing member of nonmagnetic material, and then cut apart at the interconnecting portion thereof into magnetically separated pole pieces constituting the pole piece assembly.

United States Patent Takami et a1.

METHOD OF MANUFACTURING POLE PIECE ASSEMBLY FOR ELECTROMAGNETIC TYPE PICKUP Inventors: Norihiko Takami; Osamu Hattori;

Manabu Wakabayashi, all of Toyokawa, Japan Assignee: Hitachi, Ltd., Japan Filed: May 9, 1974 App]. No.: 468,575

Foreign Application Priority Data May 11, 1973 Japan 48-51738 US. Cl 29/603; 29/418; l79/100.41 K;

l79/l00.4l D Int. Cl. Gllb 5/42 Field of Search 29/603, 602, 607, 418;

References Cited UNITED STATES PATENTS 6/1927 Bonsieur 29/418 UX [451 Aug. 19, 1975 3,092,692 6/1963 Javorik 29/603 3,163,720 12/1964 Netznik 29/607 X 3,229,355 1/1966 Hluszko 4 t 29/603 3,383,474 5/1968 Kriebel et a1. l79/10().41 K 3,828,426 8/1974 Phelon et a1. 29/418 X Primary ExaminerCarl E. Hall Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT A method of manufacturing a pole piece assembly for an electromagnetic-type pickup is disclosed. In the method a pole piece unit including a set of pole pieces integrally interconnected with each other is first punched from a sheet of magnetic material and then the punched pole pieces are bent into a predetermined shape. The pole piece unit having the predetermined shape is next fixed to a fixing member of nonmagnetic material, and then cut apart at the interconnecting portion thereof into magnetically separated pole pieces constituting the pole piece assembly.

4 Claims, 12 Drawing Figures PATENTED AUG] 9 I975 SHEET 1 IF 3 FIG. 2

PRIOR ART FHILNIEU AUG 1 75 seam 2 n5 3 FIG. 40

METHOD OF MANUFACTURING POLE PIECE ASSEMBLY FOR ELECTROMAGNETIC TYPE PICKUP FIELD OF THE INVENTION The present invention relates to a method of manufacturing a pickup assembly used for reproducing sound recorded on a disk record and, more particularly, to a method of manufacturing a pole piece assem bly forming a magnetic circuit in an electromagnetictype pickup.

DESCRIPTION OF THE PRIOR ART FIG. 1 is a schematic diagram illustrating the structure of a conventional electromagnetic-type pickup used for reproducing a stereo sound. Pole pieces are denoted by numerals l to 4, and a pair of pole pieces 1 and 3 and another pair of pole pieces 2 and 4 are connected magnetically by yokes 9 and 10, respectively. Coils 7a to 7d are mounted on a magnetic circuit consisting of the pole pieces 1 to 4 and the yokes 9 and 10.

In operation, the vibration of a stylus 6 transfers through a cantilever to an armature which might be made of a permanent magnet. The vibration of the armature 5 is then detected by the coils 7a to 7d, thereby obtaining the electrical signal corresponding to the vi bration of the armature as originated from the stylus.

A conventional method of manufacturing the magnetic circuit of such pickup will be explained with reference to FIGS. 2 and 3.

First, each of four pole pieces is punched from a thin plate of a high-permeability, and then the punched pole pieces are bent into the shape as shown in FIG. 2. The shaped pole pieces are denoted by numerals 1 to 4. These four pole pieces may theoretically be the same in shape, but, in fact, these pole pieces often take different shapes for reasons of practical operation of the pickup. Then, the so constructed pole pieces 1 to 4 are prepared with an arrangement as shown in FIG. 2, and are inserted into the slots of a holder 11 by the aid of a jig 12. An assembly after the insertion is illustrated in FIG. 3. Then the pole pieces 1 to 4 and the holder 11 are mutually secured. The connection may be made with an adhesive or by a plastic filling. After the connection of the pole pieces 1 to 4 and the holder 11 is completed, the jig 12 is removed, the coils 7a to 7d are mounted, and the respective pairs of the pole pieces are magnetically connected by yokes 9 and 10.

The method of the prior art described above has the following disadvantages:

1. Four kinds of punch dies are required for punching a thin plate of a high-permeability since four kinds of pole pieces are needed.

2. The four pole pieces take different shapes, respectively. Thus, different bending processes are required for each pole piece, which results in that the number of manufacturing steps increases and parts management is complicated.

3. The four pole pieces used for a single pickup are punched from different thin plates. Thus, there can occur a different permeability among those pole pieces. This difference of permeability causes crosstalk and unbalance between channels.

4. Since the pole piece is small, handling is difficult. When the pole piece is secured to the holder, great care must be taken for accurately positioning the four pole pieces. If such care is not taken, a disparity in finished goods may results.

SUMMARY OF THE INVENTION An object of the present invention, thus, is to provide a method of manufacturing a pole piece assembly for an electromagnetic-type pickup by which a magnetic circuit of the electromagnetic-type pickup is readily formed.

Another object of the present invention is to provide a method of manufacturing a pole piece assembly for an electromagnetic-type pickup which provides a magnetic circuit with little disparity in the performance thereof.

Another object of the present invention is to provide a method of manufacturing a pole piece assembly for an electromagnetic-type pickup, wherein management of the parts during the manufacturing process is easy.

According to the feature of the present invention, there is provided a method of manufacturing a pole piece assembly for an electromagnetic-type pickup comprising the following steps. That is, a pole piece unit including four pole pieces is punched from a thin plate of a high permeability. The punched pole piece unit is bent into a desired shape and then fixed to a holder. Finally, a part of the pole piece unit, together with a part of the holder, is cut off to provide four independent pole pieces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an example of conventional pickups.

FIG. 2 is a view for explaining a conventional method of manufacturing a pole piece assembly, in which a set of pole pieces and a holder for holding the pole pieces are illustrated.

FIG. 3 is a perspective view of the pole piece assembly constructed by the pole pieces and the holder shown in FIG. 2.

FIGS. 4A to 4E are diagramatic illustrations for explaining the manufacturing process according to an embodiment of the present invention.

FIGS. 5A to 5D are diagramatic illustrations for explaining the manufacturing process according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 4A to 4E illustrate the manufacturing process of a pole piece assembly for a electromagnetic-type pickup according to an embodiment of the present invention.

In the manufacturing process, a cross-shaped pole piece unit 13 is punched from a thin plate of a high-permeability as shown in FIG. 4A. The crossshaped pole piece unit 13 has a hole 14 within the intersection or joint portion thereof and four radially extending arms which are later separated to form magnetic pole pieces 31 to 34 are connected with each other at the intersection. The cross-shaped pole piece unit 13 is then bent into a shape such as shown FIG. 4B in such a manner that first portions of the arms, starting from the joint portion, extend parallel to each other, forming a quadrangular cup, second portions of the arms extend gradually outward from the first portions axially and radially to form a flared area, and third portions of the arms extend from the second portions in parallel to each other in the axial direction. The pole piece unit so shaped will be referred to as a bent pole piece unit and designated by numeral 16. The hole 14 may be used as a guide in the bending step. After such shaping, the bent pole piece unit is subject to a magnetic annealing in accordance with the material thereof. Then, the bent pole piece unit 16 is inserted, by the aid ofajig 17, into a hollow of a fixing block 18 of non-magnetic material, so that the bent pole piece unit 16 is so fixed as to arrange the pole pieces 31 to 34 in position.

The hollow of the fixing block 18 has a square cross section with which the jig 17 of a square cross sectional solid bar can just engage and which is provided with, on each side of the square, a groove into which the pole piece of the bent pole piece unit is just inserted, and such hollow as above is formed at the rear end side (at the right hand side in FIG. 4D) by a hollow having a shape of a frustum of a right pyramid suitable for receiving the parts of the pole pieces expanding outwardly. The fixing of the bent pole piece unit 16 to the fixing block 18 is made with an adhesive or by casting plastic onto the bent pole piece unit within the block 18.

After this fixing, the top end (denoted by a broken line 19) of the fixing block 18 and the top end of the bent pole piece unit 16 which is fixed within the fixing block are cut off by milling or surface grinding. In other words, those top ends of the fixing block and the bent pole piece unit is cut off along the broken line (FIGS. 4A, 4B and 4C) with the result that the bent unit 16 is magnetically separated into four parts, or four pole pieces 31 to 34. FIG. 4E is a front view of the fixing block fixedly provided therein with the pole pieces 31 to 34 obtained after the cutting off process. In the figure, the reference numeral 20 designates a space defined by the respective pole pieces 31 to 34 which was used to accept the jig 17 when the bent pole piece unit 16 is inserted into the fixing block 18, and which will be used to accommodate an armature such as a magnet when the pickup is assembled completely.

The subsequent steps to be taken after the four pole pieces are fixed into the fixing block through the foregoing steps, i.e. steps of mounting coils and providing yokes, are carried out in a similar manner to a conventional method.

FIGS. 5A to 5D illustrate the manufacturing process of a pole piece assembly for an electromagnetic pickup according to another embodiment of the present invention. In this embodiment, a pole piece unit 21 having a shape as shown in FIG. 5A is stamped out from a thin plate of a high permeability. The pole piece unit 21 has a hole 22 at the central portion whose surrounding portion (denoted by a broken line 23) interconnects four pole pieces. Then, the pole piece unit 21 is bent into a shape as shown in FIG. 5B. The bent pole piece unit so shaped is subjected to a magnetic annealing in accordance with the material thereof. The bent pole piece unit 24 is then secured at its front portion to a fixing block 25 of non-magnetic material, as shown in FIG. 5C. More precisely, plastic is cast onto the front portion of the bent pole piece unit 24 and is solidified. In this step, it is preferable that the fixing block 25 is provided with a hole 26 at the portion corresponding to the hole 22 of the bent pole piece unit 24. Thereafter, the bent pole piece unit 24 is separated into individual pole pieces by cutting the portion denoted by the broken .4 line 23 shown in FIGS. 5A and 5B with a drill 27 guided along the hole 26. That is, the bent pole piece unit 24 is magnetically separated into four pole pieces 41 to 44. This cutting operation may also be carried out by a reaming or an internal grinding. The subsequent steps to be taken after the four pole pieces are secured to the fixing block, i.e. steps of mounting coils and providing yokes, are performed in a similar manner to a conventional method.

The method described above according to the present invention has the following advantages:

1. A single kind of a punch die is sufficient for punching a thin plate of a high-permeability.

2. Only a single bending operation is required for four pole pieces. Thus, the manufacturing process is simplified.

3. A set of four pole pieces used for a single pickup is punched from the same sheet of a thin plate of a high-permeability. Thus, no disparity in performance among the pole pieces will occur.

4. Pole pieces are integrally interconnected before they are fixed to a fixing block. Handling and parts management with respect to those pole pieces is easy. Additionally, the relative positioning of the respective pole pieces is made with high accuracy, which results in little amount of disparity in finished goods.

From the foregoing description, it will be seen that according to the present invention an electromagnetic type pickup easily manufactured and of a good performance can be expected. We claim: 1. A method of manufacturing a pole piece assembly for an electromagnetic-type pickup, said pole piece assembly being the type having two pairs of facing pole pieces, comprising the steps of:

stamping a pole piece unit from a thin plate of magnetic material, said pole piece unit having four arms extending outwardly from a joint portion with opposite ones of said arms from said joint portion being joined symmetrically with said joint portion,

bending said four arms into a predetermined shape with said opposing ones of said arms being maintained in opposing relationship across said joint portion with respect to each other,

subjecting said pole piece unit bent is said predetermined shape to magnetic annealing,

thereafter inserting said bent pole piece unit into a fixing member of non-magnetic material, said fixing member having a hollow recess for receiving said joint portion and the bent arms of said pole piece unit thereinto,

securing said bent pole piece unit in said fixing member such that said opposing ones of said arms adjacent said joint portion are maintained in position with respect to said fixing member, and

severing said joint portion from said pole piece unit to separate said opposing ones of said arms from said joint portion, thereby forming two pairs of spaced pole pieces from said opposing ones of said arms.

2. A method as claimed in claim 1, wherein said step of bending said four arms includes bending first portions of said arms from said joint portion to extend parallel to each other in the axial direction, thereby forming a quadrangular-shaped cup, bending second portions of said arms from said first portions gradually outwardly from said first portions, both axially and radially, to form a flared area. and bending third portions of said arms from said second portions to extend in parallel with respect to each other in the axial direction, and wherein said hollow recess of said fixing member includes a first section having a square crosssection with a groove on each side wall into which said first portions of said arms are inserted, and further including a second section having a flared cross-section for receiving said flared area of said second portions of said arms, such that said step of severing forms said two pairs of spaced pole pieces from said axially extending parallel first portions of said opposing ones of said arms.

3. A method as claimed in claim 2, wherein said step of severing includes cutting off a portion of said fixing member where said joint portion is provided.

4. A method as claimed in claim 1, wherein said step of bending provides first portions of said opposing ones of said arms coplanar with said joint portion, and bends second portions of said opposing ones of said arms from said first portions into a parallel axially extending direction, said joint portion being provided with a hole at the center thereof, and wherein said hollow recess of said fixing member includes a section receiving said joint portion with said coplanar first portions of said opposing ones of said arms therein, while said second portions of said opposing ones of said arms extend outwardly from said fixing member, said fixing member including a second hole being aligned with said hole in said joint portion, such that said step of severing is effected by enlarging said holes, thereby removing said joint portion so that said two pairs of spaced pole pieces are formed from opposing ends of said coplanar first portions of said arms. 

1. A method of manufacturing a pole piece assembly for an electromagnetic-type pickup, said pole piece assembly being the type having two pairs of facing pole pieces, comprising the steps of: stamping a pole piece unit from a thin plate of magnetic material, said pole piece unit having four arms extending outwardly from a joint portion with opposite ones of said arms from said joint portion being joined symmetrically with said joint portion, bending said four arms into a predetermined shape with said opposing ones of said arms being maintained in opposing relationship across said joint portion with respect to each other, subjecting said pole piece unit bent is said predetermined shape to magnetic annealing, thereafter inserting said bent pole piece unit into a fixing member of non-magnetic material, said fixing member having a hollow recess for receiving said joint portion and the bent arms of said pole piece unit thereinto, securing said bent pole piece unit in said fixing member such that said opposing ones of said arms adjacent said joint portion are maintained in position with respect to said fixing member, and severing said joint portion from said pole piece unit to separate said opposing ones of said arms from said joint portion, thereby forming two pairs of spaced pole pieces from said opposing ones of said arms.
 2. A method as claimed in claim 1, wherein said step of bending said four arms includes bending first portions of said arms from said joint portion to extend parallel to each other in the axial direction, thereby forming a quadrangular-shaped cup, bending second portions of said arms from said first portions gradually outwardly from said first portions, both axially and radially, to form a flared area, and bending third portions of said arms from said second portions to extend in parallel with respect to each other in the axial direction, and wherein said hollow recess of said fixing member includes a first section having a square crosssection with a groove on each side wall into which said first portions of said arms are inserted, and further including a second section having a flared cross-section for receiving said flared area of said second portions of said arms, such that said step of severing forms said two pairs of spaced pole pieces from said axially extending parallel first portions of said opposing ones of said arms.
 3. A method as claimed in claim 2, wherein said step of severing includes cutting off a portion of said fixing member where said joint portion is provided.
 4. A method as claimed in claim 1, wherein said step of bending provides first portions of said opposing ones of said arms coplanar with said joint portion, and bends second portions of said opposing ones of said arms from said first portions into a parallel axially extending direction, said joint portion being provided with a hole at the center thereof, and wherein said hollow recess of said fixing member includes a section receiving said joint portion with said coplanar first portions of said opposing ones of said arms therein, while said second portions of said opposing ones of said arms extend outwardly from said fixing member, said fixing member including a second hole being aligned with said hole in said joint portion, such that said step of severing is effected by enlarging said holes, thereby removing said joint portion so that said two pairs of spaced pole pieces are formed from opposing Ends of said coplanar first portions of said arms. 